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Stepping down 200kv to 1kv

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Antonio

Sat Aug 24 2013, 02:46PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

That circuit does not make sense. The polarities, positions, and values of the components all look strange. The circuit passes a huge current directly through the ideal transformer, producing a huge power at the output. The transistor has no function.

Andy

Sat Aug 24 2013, 07:50PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

Hi Antonio, the two inductors are coupled, when the transistor closes it changes the ideal one that will handle alot of current(top one).
The idea is to make a transformer and the two inductors with really low resistance looking around 0.0001ohms, it should be doable.

radiotech, I'm still trying to understand your post, are you saying if I add a tuned circuit it will negate the effect of the capacitance to ground

radiotech

Sat Aug 24 2013, 09:55PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Your 1 Amp 200kV pulse, was sourced from a 400 kV generator in series with a 200,000 ohm resistor.

To get 200 kW power, steady state it needed to terminated in a 200,000 resistor.

To get 200 amps at 1000 volts the terminating resistor must be 50 ohms.

A transformer ratio would 63:1

This has the odor of a radar problem. Like a thyratron dumping a slug of energy from an inductor
though a pulse forming network to kick a magnetron.

Or like an EMP fixture.

Antonio

Sun Aug 25 2013, 01:38AM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

The transistor is PNP. Should be NPN, and the large resistors are not necessary. No real transistor would operate with 24 kV. The reading at the power meter is from a huge current through the 0.001 ohm resistor increased 10 times by the transformer, that is ideal and then operates with DC current too.

Andy

Sun Aug 25 2013, 02:43AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Hi Antonio, the large resistors is to divide the voltage, with that I think the voltage was like 10volt across the transistor. I don't want to much current going down that path, just the 24kv across the inductor, and dropped down for the transistor., Most of the signal on the primary of the transformer is square wave, from 24kv down to about 5kv(I think a large H on the high side makes more of a swing).

How would you go about designing a ideal transformer?

radiotech, will look at a emp source, any links

Proud Mary

Sun Aug 25 2013, 04:50PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Let us begin by considering the current path R2, L2, R1, Q1, and R8.

We will discard from our thoughts R2 - 1 mÎ© - and assume that the ohmic resistance of L2 is negligable.

And we will replace Q1 with a single pole single throw switch.

This leaves R1 and R8 as passive circuit elements totalling 100 kÎ©.

When the switch standing in for QI is open, no current will flow.

When the switch is closed, with 24 kV across the ends of this series string a current of 24,000/100,000 = 240 mA will flow.

The voltage drop across R1 will 0.24*10,000 = 2.4 kV.

And the voltage drop across R8 will be 0.24*90,000 = 21.6 kV.

If we now replace the mechanical switch with your transistor 2N3702, we have a puff of smoke, because you have a collector-base voltage of 2.4 kV, when the data sheet shows the absolute maximum for this PNP transistor is -40 V.

,d.d2k&cad=rja

Now in the case where the transistor switch is OFF, then the voltage on the collector will be your 24,000 V, and the voltage on the emitter 0V, which exceeds the maximum permitted emitter-collector voltage of -25 V by a fiery margin!

The transistor may have the good sense to act as a fuse and go open circuit before further damage results, but on the off-chance that the guts turn into a bubbling metallic mess which squirts you in the eye, you should really think about installing fuses of the right value in any circuits you build in future.

Why PNP?

Andy

Sun Aug 25 2013, 07:07PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Hi Proud Mary
The PNP was because I thought it would have faster switching times than igbt, I've seen a igbt that goes to 4800volt, not sure of the frequency . Would having a resistor in parallel with the switch so the voltage divider works, with the correct values, to limit it to 600<volts , the inductor should still see a fluctuating current?

Thanks

Antonio

Sun Aug 25 2013, 08:22PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

The PNP transistor at that position is just a diode between its collector and base. It is not acting as a switch. The ~10 V that you see at its collector comes directly from the ideal 555 oscillator. Take a look at the current of ~ 800 A through the 0.001 ohm resistor, that is increased 10 times by the transformer, producing the 19 MW at the 0.3 ohms load. Fortunately, simulated components don't become smoke...
You can't make an ideal transformer, but can approximate one with large enough inductors coupled with k=~1.

Andy

Mon Aug 26 2013, 02:29AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Thanks Antonio
How would you wire up the PNP, they way I had it was from collector to emitter, with base and emitter connected thought ground?

I've tried A different schematic to switch the high volt dc, as long as it goes to zero in part of the cycle I'm happy. The impendence of the circuit is high though

Andy

Mon Aug 26 2013, 11:25AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

What would be a good transistor to switch 240volt, using a 555 timer

Thanks

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